Mar 5 2013:
Jack, I don't know if I understood your question and/or comment but these are two different things. The sun is a source of energy and batteries are a way to store energy independently from what source is coming from.

In an ideal system you will use as many sources available and store its energy to supply the demand. Sources of energy complement each other, they do not compete.

Feb 21 2013:
For now perhaps, in time hopefully replace generators that are limited in capacity. Replace batteries that will make cars operate more efficiently. As a backup as grids become damaged and large enough renewable energy can be stored and become mobile to support areas that are affected due to an act of g-d. And also for the typical small home the cost of energy could be reduced dramatically.